U.S. Pat. No. 7,471,498, issued on Dec. 30, 2008 to the present inventors, describes a high current carrying capacitor with a thermal disconnect device. The Patent in its entirety is incorporated herein by reference and FIGS. 1, 2 and 3 of that Patent are also described below.
Referring to FIGS. 1, 2 and 3, there is shown a high current carrying capacitor, generally designated as 10. Capacitor 10 includes hollow core 18 surrounded by capacitor winding 12. Hollow core 18 is formed by a non-conducting tubular section 22 which extends slightly beyond the ends of capacitor winding 12. At opposite ends of capacitor winding 12 are two metallization layers 14 and 16.
On completion of winding 12 of the capacitor roll, the ends of capacitor winding 12 may be sprayed with a high velocity mixture of compressed air and molten fine particles of tin produced from an electric arc gun. This spray forms opposing metallization layers 14 and 16, which may be considered electrically the same as opposing first and second terminals of the capacitor. Wire leads 23 and 25 may then each be bonded to respective metallization layers 16 and 14 by way of solder terminals 26 and 27. Metallization layers 14 and 16 completely encircle the outer circumferences of the capacitor roll.
Capacitor winding 12 is wound around tubular section 22 in conventional manner. Hollow core 18 may be trimmed to extend approximately 0.2 to 0.3 inches beyond metallization layers 14 and 16, thereby forming core extensions or collars 11 and 13. The core extensions, however, are not necessary.
As best shown in FIG. 2, tubular section 22 includes an inner surface forming the hollow core. This inner surface may be used for anchoring the tubular section to a winding machine. The tubular section is then used as a mandrel for winding the film capacitor into a roll.
Fuse 28 together with wire leads 21 and 23 are inserted into hollow core 18. As shown, fuse 28 is in a closed position which permits electrical current to flow from wire lead 21 to wire lead 23. In turn, electrical current may flow from wire lead 23 to metallization layer 16 and into a first end metallic winding of capacitor 10 by way of solder terminal 27. Furthermore, electrical current may flow from a second end metallic winding of capacitor 10 to wire lead 25 by way of metallization layer 14 and solder terminal 26. In this manner, when fuse 28 is in a closed position, capacitor 10 permits current to flow between terminals 20 and 24.
Tubular section 22 may be formed from a non-conductive material, such as polypropylene. Tubular section 22 forms a continuous passageway through the entire length of hollow core 18. As an example, the diameter of hollow core 18 may be approximately ½ an inch.
When electric current is passed through capacitor winding 12, thermal energy is generated raising the temperature of capacitor winding 12. The hottest region of capacitor winding 12 is at its geometric center. The geometric center includes the region containing tubular section 22 and is located at the radial center and the axial center of the hollow core. Thus, hollow core 18 passes directly through the region containing the highest temperature within capacitor winding 12. This region is also referred to herein as the hot spot of the capacitor winding.
Fuse 28 is disposed at the middle of the axial length of hollow core 18. In this manner, fuse 28 senses the highest temperature, or the hot spot of capacitor winding 12. As shown in FIG. 1, fuse 28 is suspended within hollow core 18, without need to fasten the fuse to any portion of the tubular section. The fuse may be centrally positioned within hollow core 18 with the aid of wire leads 21 and 23.
The present invention includes a thermal switch (also referred to herein as a fuse, or a thermal cutoff device) for a wound film capacitor, which is different from the prior art, as described below. The present invention also includes a light indicator which is controlled by the thermal switch and provides a visual alert to a user.